Forms feed mechanisms function to synchronize movement of a paper sheet, web or the like, through a printer. A pair of laterally spaced, shiftable forms feed tractors are mounted on the forms handling section of a printer so that they can be set in positions determined by the lateral width of the forms being fed, and function to facilitate the movement of paper past a print head. The pair of tractors comprise elongated molded plastic or metal housings, through which projects by way of suitable bushings, a support shaft which extends laterally across the printer. The tractors employ a releasable friction clamp for locking the left and right tractors at laterally spaced positions on the support shaft to define the path of the print medium form being fed through the printer. Further, conventionally, an endless belt is mounted on each of the housings, to its lateral outside within an appropriate track. The endless belt, is provided with semicircular bars on its inner periphery which are received within the valleys between sprocket teeth of a sprocket, mounted for rotation at one end of the elongated housing within the elongated housing, about which the endless belt is engaged. A drive shaft, projects laterally across the printer, through the sprockets and engages both sprockets to drive the endless belts for the left and right tractors respectively from a common drive motor coupled to the drive shaft. Pins projecting outwardly from the endless belt at right angles to the outer surface of the belt enter pre-punched holes on the endless form record media along both sides thereof, and as the pins move, they carry the paper forwardly through the printer.
U.S. Pat. No. 4,226,353, issued Oct. 7, 1980, to Silvio U. Blaskovic et al, and assigned to the common assignee, shows a continuous forms feed tractor of this type. Typically, the front end of the elongated housing (relative to the feed path of the endless forms record media) is in juxtaposition to a rotating, cylindrical platen. The continuous forms record medium contacts the periphery of the platen for rotation therewith, past a confronting print head just upstream of the point where the perforations of the endless forms record media engage the endless belt pins of the forms feed tractors.
To maintain engagement between the continuous forms record medium and the paired endless belts carried respectively by the left and right tractors, each of the tractors have mounted thereto, to the lateral outward side of the endless belt, a door which pivots from a generally upright, forms access position, to a door closed position where the door overlies the endless belt, and functions to sandwich the endless forms record medium, in the area of the perforations, against the top of the elongated housing of the forms feed tractors.
In U.S. Pat. No. 4,226,353, the door is pivotally mounted by means of pivot pins fixed to the door at respective ends and pivotally mounted within snap fit slots of flanged receivers projecting outwardly and upwardly of the elongated housing. Additionally, one or more coil springs are connected between the elongated housing and the pivotable door, at a point above the pivot axis defined by the pins carried by the door. Further, stops are formed on the flanged receivers for ensuring that when the doors are open, they rotate such that the springs pass through the centers of rotation of the door pivot mounting pins, thereby ensuring that the doors are maintained in their upright or raised position under an overcenter action to prevent inadvertent closure.
Such continuous forms feed tractors have operated adequately in feeding continuous forms record media through wire or other type printers, however, there is a current need for such printers to randomly print on other than such continuous forms utilizing edge perforations as positive drive feed of the forms through the printer. Attempts have been made to facilitate the feeding of record media such as letter-size or legal-size paper sheets through the printer. IBM Technical Disclosure Bulletin, Volume 23, No. 7B, of December, 1980 to M. F. Davis, Jr. et al shows a cut-forms guide in the form of a chute 10 mounted to a horizontal front pivot rod of a forms wire rack assembly. This permits the chute to be adjusted to and fixed at an appropriate print position with the left edge of the guide becoming the left side of the paper, thereby assuring consistent forms feed into the pressure roll assembly when loading forms.
In at least one IBM Series/1 4974 commercial printer, a specially formed, molded plastic cut form chute assembly is insertably installed on positioning studs of the printer, after removal of the continuous form tractor assembly, to facilitate the use of cut forms type record media in lieu of the continuous forms type having the perforated edges. While the cut forms chute as a installable unit functions adequately to feed cut forms such as letter-size or legal-size paper of predetermined width, the substitution and replacement of the cut form chute for the continuous form tractor assembly and vice versa is fairly complicated and requires a series of steps to replace one for the other, to the inconvenience of the operator of the printer.
It is therefore a primary object of the present invention to provide an improved continuous forms feed tractor having the capability of handling all of the present forms currently specified for use in a standard continuous forms feed device, plus cut forms such as IBM punch cards, legal-size and letter-size paper sheets and the like without the necessity to add, subtract or substitute components to the printer itself, and without compromising the continuous forms feed mechanism of the printer.